FIX: Bug fix for TNx

[DamienIrving]

Pull Request to resolve #242

• [ ] Unit tests cover the changes.
• [ ] These changes were tested on real data.
• [ ] The relevant documentation has been added or updated.
• [ ] A short description of the changes has been added to doc/source/references/release_notes.rst.

Describe the changes you made

There's one line in the code where indicator=GenericIndicatorRegistry.Minimum needs to be changed to indicator=GenericIndicatorRegistry.Maximum.